Apparatus for cathodically protecting reinforcing members and method for installing same

ABSTRACT

A novel method and apparatus for cathodic protection of reinforced concrete structures includes an anode structure having an electrically conducting tape that is prevented from directly contacting the surface of the concrete structure. An electrically conducting coating is applied over the tape and in contact with the concrete surface to form an anode electrically connected to the tape and the concrete surface. The tape may conveniently employ a commercially available graphite tape with an adhered, electrically insulating backing. A preferred electrical connection to the tape includes a bus bar that compresses the tape by means of a screw engaging a masonry anchor mounted in the concrete structure. Preferably, the bus bar screw also mounts an electrically insulating junction box to the concrete surface to enclose the anode connection. The junction box may also cover an opening in the concrete surface through which the cathode connection to a reinforcing member is made. Wires connected to the terminals of a direct current power supply which provides the cathodic protection current are supplied to the junction box through which connections to the tape and cathode are made.

BACKGROUND

This invention concerns a method and apparatus for inexpensively andeffectively cathodically protecting reinforcing members in reinforcedconcrete structures. In particular, the invention concerns an anodestructure comprising an electrically conducting tape disposed on aelectrically insulating backing. The backing is directly applied to aconcrete structure and the tape and backing are held in place by anoverlying, electrically conducting coating that completes the structure.

The corrosion of reinforcing members, which are ordinarily made ofsteel, in reinforced concrete structures such as bridge piers, decks andrailings, parking garage floors, etc., is a constant problem. Inclimates where snow and ice accumulate, the brine produced byice-melting salts induces and accelerates the corrosion problem.Salt-accelerated corrosion is also encountered in coastal areas wheresalt water contacts reinforced concrete structures. Chloride ionsaccelerate the corrosion of steel reinforcing members and help generatecorrosion products that occupy a larger volume than the uncorrodedsteel. The corrosion products create severe internal pressure on theconcrete resulting in cracking and spalling. Once cracking and spallingbegin, access to reinforcing members increases, further accelerating therate of corrosion, cracking and spalling.

Cathodic protection is a well known and effective method of combatingcorrosion in reinforced concrete structures. In cathodic protection, asmall electrical current supplied by an external direct current powersource flows from an anode disposed on the surface of the concrete tothe reinforcing members within the concrete structure which act as acathode. This current flow counteracts the electrical current that wouldflow in the course of electrochemical corrosion of the reinforcingmembers and inhibits the electrochemical corrosion reaction. Thenegative sense terminal of the external power supply is connected to thereinforced structure by exposing a reinforcing member at one or morelocations so that the necessary electrical connections can be made. Theopenings are then covered with fresh concrete, grout or another materialto protect the reinforcing members.

A number of techniques for making anode connections to reinforcedconcrete structures are known. A typical connection is disclosed in U.S.Pat. No. 4,255,241 to Kroon et al. for "Cathodic Protection ApparatusAnd Method For Steel Reinforced Concrete Structures". There, an anode isformed in a slot sawn into the concrete structure. An insulator isdisposed on the innermost surface of the slot. The slot is then filledwith an electrically conducting material in which is suspended aplatinized niobium wire. The remainder of the slot is filled with aninert material so that a surface flush with the original surface of theconcrete is formed.

Known anode structures, like those disclosed by Kroon, require anexpensive platinized niobium wire. The installation process for thoseanode structures requires a significant amount of expensive labor.Accordingly it is desirable that a cathodic protection system forreinforced concrete structures employ an anode structure that isinexpensive both in materials cost and the cost of installation.

SUMMARY OF THE INVENTION

The present invention employs low cost materials and a simpleinstallation method for an anode structure and for apparatus forcathodic protection of reinforcing members in reinforced concretestructures. The anode structure is constructed on site in the course ofits installation. In a preferred embodiment, the only working ofconcrete on site during installation of an embodiment of the inventionis simple drilling.

In a preferred embodiment of the invention, the anode structurecomprises an electrically conducting tape disposed on an electricallyinsulating backing or substrate. The tape may preferably be acommercially available graphite tape with or without an adhered paperbacking. The tape is applied to an insulating backing, if necessary, andthe backing is placed in contact with the concrete surface of thestructure to be protected. In order to hold the tape and/or backing inplace permanently, an electrically conducting paste, or relativelyviscous fluid, is spread on the top of the tape and on the adjacentareas of concrete. This conductive material may be commerciallyavailable mastic or polymer that is filled with electrically conductingparticles. Alternatively, an electrically conductive coating may beapplied to the tape and adjacent concrete surface. It is important thatthe tape not directly contact the concrete. The insulating backingprevents deterioration of the tape as the cathodic protective currentflows. The tape provides the electrical connection between the powersource and the anode formed by the electrically conductive materialapplied in the field. The resistivity of the adhesive or coating may belower than that of the tape.

The cathode connections to the reinforcing members can be made in theconventional way. However, in a preferred embodiment, the novelapparatus includes a junction box that is directly mounted on theconcrete surface to protect the electrical connections. Before mountingthe junction box, access to a reinforcing member is gained by drillingor some other technique and the cathodic connection is made. Preferably,the junction box is mounted to cover the opening communicating with theexposed reinforcing member. The wire connecting the power supply to theexposed reinforcing member preferably passes through the box to thereinforcing member. In a preferred embodiment, the electricallyconducting tape of the anode structure is terminated by a compressionconnector which includes a bus bar that clamps an end of the tape. Thecompression connection is preferably disposed within the junction box.It is preferred that the compression member mount on the concretesurface and that its mounting also provide mounting support to thejunction box.

The remainder of the apparatus, namely a direct current power source andelectrical connections from the source to each junction box, isconventional. Conventional conduit may be used to carry the power linesfrom the source to the electrodes of the apparatus. A pluality of anodestructures according to the invention may be disposed at variouslocations over the surface of a reinforced concrete structure,preferably each disposed near a cathodic connection to a reinforcingmember.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 is a side view of a pier structure made of reinforced concreteand having an embodiment of the apparatus according to the inventioninstalled on it;

FIG. 2 is a front view of a reinforced concrete wall having anembodiment of the apparatus according to the invention mounted on it;

FIG. 3 is a front view of a junction box, with the front cover removed,illustrating one embodiment of electrical connections to the electrodesaccording to the invention;

FIG. 4 is a sectional side view of a junction box mounted on areinforced concrete surface and depicting an embodiment of electrodeconnections according to the invention;

FIG. 5 is an exploded view of an embodiment of a termination of an anodestructure according to the invention; and

FIG. 6 is a sectional side view of the construction of an anodestructure according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In all of the drawing figures, like elements are given the samereference numbers.

In FIG. 1 a typical application of an embodiment of the invention isshown. There, three piers 1, constructed of reinforced concrete, supporta generally horizontal pier cap 3 also constructed of reinforcedconcrete. As is conventional, piers 1 are supported on subterraneansupports (not shown) below grade level 5. An anode structure 7 isdisposed on each of two opposing faces of each of piers 1 extending fromjust above grade level 5 to near pier cap 3. Just beneath pier cap 3,each of anode structures 7 enters a junction box 9 which is shown ingreater detail in FIGS. 3 and 4. Another anode structure 7 is disposedgenerally horizontally on a surface of pier cap 3 and enters a junctionbox 9 disposed at one end of pier cap 3. As explained below, each ofjunction boxes 9 preferably encloses an electrical connection for theanode structure and protects the electrical connection to the cathode,which is the framework of electrically conducting reinforcing memberswithin the concrete structure.

Direct current electrical power is supplied to the anodes and cathodesof FIG. 1 by a power source 11 mounted on one of piers 1. Electricalpower is distributed from source 11 in a conventional way through wirescontained in a conduit 13 indicated by dashed lines in FIG. 1. Theconduit is mounted on the concrete structure in a conventional manner.Power supplies for use in cathodic protection systems are available fromHarco Corporation, Medina, Ohio and other suppliers.

In FIG. 2, a reinforced concrete retaining wall or pier 15 that iscathodically protected by an embodiment of the invention is shown. Anumber of generally vertically disposed anode structures 7 are spaced onthe face of wall 15. A generally horizontally disposed anode structure 7is attached to wall 15 near its top. Each of anode structures 7 isterminated within a junction box 9 through which cathode connections tothe reinforcing steel network are also preferably made. Conduit 13contains electrically interconnecting wires for the anodes and cathodesto connect them to a direct current power source 11 also mounted on wall15. Conduit 13 is indicated by a dashed line although it isconventionally a pipe or tube that resists corrosion.

Turning to FIG. 6, a detailed sectional view of anode structure 7according to the invention of FIGS. 1 and 2, is shown mounted on thesurface of a reinforced concrete structure 21. The portion of theconcrete structure 21 shown in FIG. 6 includes an external surface 23 onwhich the novel anode structure is mounted. The anode structurepreferably comprises an electrically conductive tape 27 disposed on anelectrically insulating backing 29 that is in direct contact withconcrete surface 23. The term tape as used here generally refers to aconductor having in cross section a first dimension that is larger thana second dimension that is transverse to the first dimension. In apreferred embodiment, the tape may have a generally rectangular crosssection; however, the invention is not limited to a conductive tapehaving a particular cross sectional configuration.

Preferably, electrically conducting tape 27 is formed from a low costmaterial rather than the platinized niobium wire that is now used incathodically protected reinforced concrete structures. We have foundthat a commercially available graphite thread sealant tape sold underthe trademark GRAFOIL by Union Carbide Corporation is a suitablematerial for anode tape 27. The composition and method of making theGRAFOIL tape is described in U.S. Pat. No. 3,404,061 to Shane et al. for"Flexible Graphite Material Of Expanded Particles Compressed Together".This sealant tape may include an electrically non-conductive backingadhered to one face of the tape that is useful as insulating member 29shown in FIG. 6. The tape is commercially available in a number ofthicknesses and widths.

GRAFOIL is also available as a valve packing material without anelectrically insulating backing. Graphite tape without an insulatingbacking may also be used as tape 27 of anode structure 7 provided thatan electrical insulator is interposed between the conducting tape andconcrete surface 23. It is important that the insulating substrate bepresent since the electrical conductor used in the invention is moreelectrochemically active than the expensive platinized niobium wire thathas been used in known cathodic protection apparatus. Thus the conductoris more susceptible to erosion from electrical current flow than isplanitized wire. By preventing direct contact between tape 27 andconcrete surface 23 with insulator 29, the erosion that could result ifthere were direct contact is avoided. It follows that insulator 29 couldbe of a smaller area per unit of length than tape 27, but that it ispreferred that insulator 29 have at least the same area per unit oflength as the tape 27 to prevent direct contact between the tape andconcrete surface 23.

Some means must be provided to hold tape 27 and insulator 29 in thedesired location on concrete surface 23 and to make the anode connectionfrom tape 27 to surface 23. It is preferred that the fixation andconnection means be an electrically conducting material 30 that isapplied on the exposed surface of tape 27 and along its sides to extendbeyond the tape and contact concrete surface 23. (Because FIG. 6 is asectional side view, the portion of material 30 extending to surface 23is not readily apparent in that Figure.) This overlying electricallyconductive material, the anode, is preferably not interposed betweeninsulator 29 and surface 23. It is important that the overlyingconductive material, the anode, have a relatively low electricalresistivity so that it spreads the anodic current conducted by the tapeand discourages erosion of the tape by electrical currents.

Electrically conductive materials that form suitable anodes arecommercially available as mastics, polymers and other coatings. Thesemastics, polymers and coatings can be applied to the tape by spraying,brushing, troweling or other conventional means. Once the electricallyconducting coating forming the anode cures, it is usually effective inholding the anode structure in place and providing the necessaryelectrical connection.

Separate electrical connections must be made to the tape that supplieselectrical current to the anode and to the reinforcing members of theconcrete structure, the cathode, from power supply 11. In a preferredembodiment, a junction box 9, shown in detail in FIGS. 3 and 4, enclosesthe tape connection and protects both the positive and negativeconnections from the weather. Junction box 9 includes an aperture 31through which electrical leads from direct current power supply 11enter. Aperture 31 is weatherproofed with an appropriate fitting orgrommet 33. Preferably, junction box 9 is mounted directly on surface 23of the concrete structure and includes an opening 35 in the surface ofthe box that contacts structure 21.

Before mounting of box 9, an opening is made in concrete 21 from surface23 to gain access to a reinforcing member 39 in order to make thecathode connection. Opening 37 may be made in a conventional manner suchas hammering and chipping or, preferably, simple drilling. Once accessto member 39 is gained, an electrical connection 41 between reinforcingmember 39 and a wire 42 connected to the negative sense terminal ofpower supply 11 is made in a conventional manner known to those skilledin the art. The area of opening 37 in surface 23 is preferably smallerthan the area of the rear wall 47 of junction box 9 so that box 9 maycover the opening and protect the cathodic connection from weather. Ifdesired, box 9 may include a peripheral gasket or caulking (not shown)to provide additional protection against weather.

A preferred embodiment of an electrical connection to tape 27 is shownmost clearly in FIGS. 4 and 5. Tape 27 emerges from anode 30 just belowbox 9 and enters the junction box through an aperture 43, best seen inFIG. 3. Electrical connection to the tape is made by a compressionconnector shown in FIG. 5. The compression connector includes anelectrically conducting bus bar 45, preferably made of copper or someother metal that makes a low resistance contact to tape 27. Tape 27 ispreferably disposed between one side of bus bar 45 and back wall 47 ofjunction box 9. To avoid shortcircuiting, junction box 9 is preferablymade of an electrically insulating material. Tape 27 is curled over busbar 45 and contacts both opposed surfaces of the bus bar. Tape 27 isclamped to bus bar 45 by an optional strap 49 which may be an electricalinsulator or conductor. In the embodiment illustrated, strap 49compresses tape 27 against bus bar 45 by means of two screws 51 thatpass through junction box back wall 47 to engage masonry anchors 53 thathave been previously installed in holes drilled in concrete 21 throughsurface 23. Not only do screws 51 clamp tape 27, but they also provide ameans of mounting junction box 9 to concrete structure 21. If strap 49is omitted, bus bar 45 clamps tape 27 only against back wall 47 ofjunction box 9. This pressure provides a satisfactory electricalcontact. When strap 49 is present, tape 27 is clamped in two locations,improving reliability.

Screws 51 and/or anchors 53 are made of an insulating material, such asplastic, to avoid creating a high conductivity electrial path directlybetween tape 27 and concrete 21. An electrical connection from powersupply 11 to bus bar 45 is made in a conventional manner. In theembodiment shown, a conductor 55 connected to the positive senseterminal of power supply 11 is terminated in an eyelet 57. Eyelet 57 isheld against bus bar 45 by means of a bolt 59 that passes through a holein bus bar 45 and through eyelet 57 to engage a nut 61. The electricalconnection embodiments shown are inexpensive to make, easy to installand reliable.

A particular advantage of the embodiment of the invention described isthe simplicity with which it may be installed. Once the desiredlocations of the anode structures and junction boxes are identified, theconcrete structure is opened at each of the junction box locations togain access to a reinforcing member for the cathode connection.Although, in general, the reinforcing members are all electricallyconducting and in electrical communication with each other, it ispreferred to make multiple electric connections to the reinforcingmembers to avoid excessive resistive losses. Once the openings have beenmade, it is preferred that the surfaces on which the anode structuresare to be disposed be cleaned for establishing good adherence andelectrical contact between the anodes and concrete. The surfaces may becleaned by scrubbing with a detergent, spraying with a mild etchant andrinsing or, preferably, lightly sandblasting the anode contact area.Thereafter, the conductive tape is applied and temporarily held inplace, for example with pressure sensitive adhesive tape, until theelectrically conductive material is applied to the tape and adjacentconcrete surface. Use of a conducting tape with an adhesive insulatingbacking simplifies the installation procedure. However, use of aseparate insulating substrate does not unduly complicate installation ofthe structure. The electrical connections to the direct current powersource can then be connected and the junction box mounted in previouslyinstalled masonry anchors.

No cutting of slots or removal of substantial amounts of concrete isrequired to install the illustrated embodiment of the invention. Aspreviously mentioned, additional steps may be taken to seal the junctionbox to the concrete surface, such as caulking. While the openingprepared in the concrete to make the cathodic connection could be filledwith concrete, a grout or another insulating material, it is preferableto leave the opening empty so that easy access to the cathode connectionis available, if necessary. Should servicing or replacement of the anodestructure be necessary, all parts of it are readily accessible forremoval or repair.

The invention has been described with respect to certain preferredembodiments. Various additions and other modifications within the spiritof the invention will occur to those of skill in the art. Accordingly,the scope of the invention is limited solely by the following claims.

We claim:
 1. An anode structure for use in apparatus for cathodicallyprotecting electrically conducting reinforcing members in a reinforcedconcrete structure comprising:an electrically conductive graphite tapehaving a first electrical resistivity, for conducting a cathodicprotection current from a direct current power source; an electricallyinsulating backing disposed between said tape and a surface of areinforced concrete structure to be cathodically protected, forpreventing direct contact of said tape with said surface; and anelectrically conductive anode coating disposed on said tape and on saidsurface adjacent the tape for conducting a cathodic protection currentto said reinforcing member.
 2. The anode structure of claim 1 whereinsaid backing comprises paper adhered to said graphite tape.
 3. The anodestructure of claim 1 wherein said anode coating comprises anelectrically conductive mastic.
 4. The anode structure of claim 1wherein said anode coating comprises an electrically conductive polymer.5. The anode structure of claim 1 including termination means for makingan electrical connection to said tape.
 6. The anode structure of claim 5wherein said termination means comprises a bus bar for electricallycontacting said tape and means for compressing said bus bar against saidtape.
 7. The anode structure of claim 6 wherein said bus bar includes atleast one hole and said means for compressing includes a fastener forpassing through said hole and engaging an anchor mounted in saidreinforced concrete structure.
 8. The anode structure of claim 7including junction box for enclosing said termination means, saidjunction box means containing an aperture for passage of said tape intosaid box means.
 9. The anode structure of claim 8 wherein said junctionbox means is made of an electrically insulating material.
 10. Anapparatus for cathodic protection of electrically conducting reinforcingmembers in a reinforced concrete structure, said apparatus comprising:anelectrically conductive graphite tape having a first elecrtricalresistivity for conducting a cathodic protection current from a directcurrent power source; an electrically insulating backing disposedbetween said tape and a surface of a reinforced concrete structure to becathodically protected, for preventing direct contact of said tape withsaid surface, an electrically conductive anode coating disposed on saidtape opposite said backing and on said surface adjacent to said tape forconducting a cathodic protection current to said reinforcing member; anddirect current electrical power source means for supplying a cathodicprotection current and having positive and negative polarity terminals,said negative polarity terminal electrically connected to saidreinforcing member of said structure and said positive terminalelectrically connected to said tape.
 11. The apparatus of claim 10wherein said backing comprises paper adhered to said graphite tape. 12.The apparatus of claim 10 wherein said anode coating comprises anelectrically conductive mastic.
 13. The apparatus of claim 10 whereinsaid anode coating comprises an electrically conductive polymer.
 14. Theapparatus of claim 10 including termination means for making anelectrical connection to said tape means.
 15. The apparatus of claim 14wherein said termination means comprises a bus bar for electricallycontacting said tape and means for compressing said bus bar against saidtape.
 16. The apparatus of claim 15 wherein said bus bar includes atleast one hole and said means for compressing includes a fastener forpassing through said hole and engaging an anchor mounted in saidreinforced concrete structure.
 17. The apparatus of claim 16 includingjunction box means for enclosing said termination means, said junctionbox means containing an aperture for passage of said tape into said boxmeans.
 18. The apparatus of claim 17 wherein said junction box means ismade of an electrically insulating material.
 19. The apparatus of claim15 wherein said junction box means includes a second opening forreceiving wires electrically connected to said power source means and athird opening for passing one of said wires out of said box means forelectrical connection to one of said reinforcing members.
 20. A methodof installing an anode structure on a reinforced concrete structurecontaining electrically conducting reinforcing members to becathodically protected comprising:applying an electrically conductivegraphite tape having a first electrical resistivity and an electricallyinsulating backing to a surface of a reinforced concrete structure to becathodically protected so that said backing is disposed between saidtape and said surface and said tape does not directly contact saidsurface; and applying an electrically conductive anode coating having anelectrical resistivity smaller than said first electrical resistivityover said tape and on said surface adjacent said tape.
 21. The method ofclaim 20 including cleaning the surface of said structure where saidcoating and backing are to be disposed before applying said backing. 22.The method of claim 20 including electrically connecting the positiveterminal of a direct current power supply to said tape.
 23. The methodof claim 22 including connecting said tape by compressing it with a busbar by mounting said bus bar to said structure.
 24. The method of claim23 including mounting an electrically insulating junction box containingsaid bus bar to said structure simultaneously with mounting said busbar.
 25. The method of claim 24 further including removing concrete fromsaid structure to expose a reinforcing member and electricallyconnecting the negative terminal of said direct current power supply tosaid exposed member.